I am using a new Mac mini. I cannot change my AirPort network name. How can I change it? When I go to AirPort Utility, it says "unable to find wireless devices". It says $guest$ by default.
What kind of device is publishing the wireless network you're trying to connect to? AirPort Utility is for configuring an Apple AirPort Extreme, AirPort Express, or Time Capsule. If you have a different brand of wireless router that's publishing this network called "$guest$", you need to read the manual for that other device to find out how to reconfigure it.
If there's a different network you want your Mac to join, click on the AirPort "radio waves" icon menu in the menu bar. It will show you a list of wireless networks within range (at least the ones that don't try to hide their network name). Then you can select one from the list and your Mac will try to join it.